Fortran Wiki
cpu_time

Description

Returns a real value representing the elapsed CPU time in seconds. This is useful for testing segments of code to determine execution time.

If a time source is available, time will be reported with microsecond resolution. If no time source is available, time is set to -1.0.

Note that time may contain a, system dependent, arbitrary offset and may not start with 0.0. For cpu_time, the absolute value is meaningless, only differences between subsequent calls to this subroutine, as shown in the example below, should be used.